Many systems are known for locking and subsequently unlocking doors, such as those used for motor vehicles, residences and other buildings. Conventional key systems have proven to be easily defeated by sophisticated thieves. As a result, a number of keyless entry systems have been introduced. However, over time, may of these systems have also been circumvented.
Conventional security systems exhibit a number of additional disadvantages. Some employ alarms which may be activated prematurely by unintended movement of the car, and which may be disabled by a knowledgeable thief. Certain keyless entry systems have employed remote radio transmitters. These systems tend to be rather complex and expensive and have not worked as reliably as required. Coded security systems are also rather complex and expensive. Moreover, it can be time consuming and tedious to operate a coded system, particularly at night or in the dark. And, if the code is forgotten, the person seeking entry can be stranded outside of the door.
Unless a keyless entry transmitter employs a fairly weak signal, its batteries will soon die. To compensate for this weak signal a large, bulky antenna must be utilized. Alternatively, the transmitter can be turned off between uses. However, this requires the user to reach into his or her pocket, purse, bag, etc. to activate the system.
A known identification system disclosed by published U.K. patent publication 2,129,176 employs a portable device such as a wrist watch that is placed in direct contact with the skin. The watch transmits a selected code through the user's body, which code is received by a touch element having decoding circuitry. Due to the weak signal that is generated, this apparatus only operates when the transmitter directly engages the skin. If the transmitter is separated from the skin (for example, when in a purse or brief case) the device does not work because the receiver does not exhibit sufficient gain to enable proper detection of the transmitted signal. Additionally, the British device employs a conventional battery to power the transmitter. Such batteries wear out in time and must be replaced. If a replacement battery is not accessible, the system is rendered inoperative.